In Generations I, II, III, and VII, the Cerulean Gym is designed like an indoor swimming pool, with platforms above the water for the player to walk on. In Generation IV, the Gym consists of a large pool roped off into lanes with certain parts of the area circling the pool blocked. There are no puzzles to solve in this Gym.

In Generations II and IV, Misty isn't initially at the Gym. After the problem at the Power Plant has been fixed, she can be found at Cerulean Cape, having a date with her boyfriend. After her boyfriend is scared away by the player's arrival, Misty will at first be angry at the player for ruining her date, but will then return to the Gym, allowing it to be challenged.

In the anime

In the main series

Cerulean Gym's original design

Cerulean Gym's aquarium

The Gym's original battlefield

Cerulean Gym has appeared in multiple episodes of the anime. In its original design, the building was a dome-shaped, brightly colored Gym with a gigantic painting of a Dewgong on top of it. On the inside, the Gym was seen being equipped with a large aquarium and a swimming pool. In the Sun & Moon series, the Gym seemed to have gone through a massive redesign in-between appearances, both on the exterior and the interior. For example, the battlefield is now a stone field, which can be retracted into the floor and filled with water to form a water field, suitable for the Gym's Water-type Pokémon.

It first appeared in The Water Flowers of Cerulean City. Ash was heading there so he could earn his Cascade Badge. Misty kept telling him not to go to Cerulean, and he soon discovered why she tried to stop him; her three sisters, Violet, Lily, and Daisy, were the Gym Leaders. However, they had turned the battlefield into a performance hall for their water acrobatics shows. Incapable of giving Ash a proper Gym battle, they were about to simply give Ash the Badge when Misty intervened. She challenged Ash to a battle in her capacity as an official Gym Leader in the games, but it was interrupted by Team Rocket. In the end, Daisy gave Ash the Cascade Badge, saying that if it weren't for him, the Gym would have been destroyed.

The Gym's next appearance was in The Misty Mermaid. While on the way to the Viridian Gym, Misty's Horsea had become sick. Realizing the Gym was nearby, Misty decided to go and see if they could make Horsea feel better. The Dragon Pokémon felt better immediately. However, the sisters made Misty participate in one of their water ballet shows. During a Team Rocket battle, the Seel the Sensational Sisters had in their first appearance evolved into Dewgong and saved the Gym. Before leaving, Misty left her Horsea and Starmie at the Gym, hoping one day to come back for them.

The Gym reappeared hundreds of episodes later in When Regions Collide!, where Ash and his classmates from Alola visited it during an extracurricular lesson, guided by Brock and Misty. After giving a brief summary to Ash's classmates about how Gyms, Badges, and the Pokémon League work in Kanto, the group was offered to experience a Gym battle. First Mallow and Lana took on Misty, after which Sophocles and Lillie battled against Brock. After both of these battles had ended with no clear winner, Kiawe requested to have a serious battle against Brock, while Ash issued a similar challenge to Misty. During the battle between Kiawe's Turtonator and Brock's Steelix, the former Pewter GymLeaderMega Evolved his Pokémon as a response to Kiawe's decision to use his Z-Move. Although Turtonator's Inferno Overdrive dealt heavy damage on Mega Steelix, it was unable to deal the finishing blow, allowing Brock to win the battle with his next attack. In the following battle between Ash's Pikachu and Misty's Gyarados, the Cerulean Gym Leader also demonstrated her ability to use Mega Evolution. However, unlike Kiawe, Ash was able to use his own Z-Move, Gigavolt Havoc, to defeat his Mega Evolved opponent. Before Ash and his classmates headed back to Alola, Brock and Misty gave each of them a replica Badge to remember the battles they had had with them.

Used by Daisy, Violet, and Lily

Dewgong first appeared as a Seel, holding out the Cascade Badge, when Ash was about to challenge the Sensational Sisters. Later, Seel was one of the Pokémon performing in a play hosted by the sisters. It evolved into a Dewgong while battling Jessie's Arbok.

Lily has her own Goldeen as her only known Pokémon. She sent it out briefly to show Ash that it was the only Pokémon that she had left after she and her two other sisters were beaten by the three other Trainers from Pallet Town.

Pokémon used in Gym

In the manga

In The Electric Tale of Pikachu manga

Cerulean Gym in The Electric Tale of Pikachu

Cerulean Gym battlefield in The Electric Tale of Pikachu

The Cerulean Gym appeared in Play Misty For Me. After defeating Brock rather easily, Ash was confident of his abilities, and headed to Cerulean City in order win his second Badge. At the Gym, Ash met Daisy, Lily, and Violet, who briefly talked about which one of them would battle Ash, until Misty arrived, declaring that she'd battle him.

At the Gym's water battlefield, Misty revealed her Pokémon to be Gyarados, which proceeded to snatch away Ash's hat. Misty declared that if Ash would be able to get his hat back from her, she'd give him the Cascade Badge. With Pikachu being too scared of Gyarados, Fearow being asleep, Pidgeotto being away, and Metapod only being capable of using Harden, Ash's chances for succeeding in the given task seemed nonexistent. However, Metapod then suddenly evolved into Butterfree, allowing Ash to put Gyarados asleep with Butterfree's Sleep Powder. Although Pikachu was now willing to move, Misty distracted the Electric Mouse with a rice ball before it could get the hat back. Ash countered by throwing a soy sauce-covered dumpling at Misty, causing his dumpling-loving Fearow to snatch the hat away from her. As promised, Misty's sisters then rewarded Ash with the Cascade Badge, despite Misty trying to protest that Ash's victory was a fluke.

Cerulean Gym in Pokémon Adventures

Cerulean Gym in Pokémon Pocket Monsters

Cerulean Gym in Pokémon Zensho

In the Pokémon Adventures manga

The Cerulean Gym appeared in Suddenly Starmie, where Red and Misty trained together at the Gym for a few days to improve their skills in order to fight Team Rocket. After the training was complete, Misty gave Red a Cascade Badge.

In the Pokémon Pocket Monsters manga

The Cerulean Gym appeared in Obtain the Moon Stone!!, where Red and his Pokémon fought Misty in order to obtain the Moon Stone she had with her. In the manga, Cerulean Gym is depicted in a very traditional Japanese architectural style.

In the Pokémon Zensho manga

The Cerulean Gym appeared in Cerulean City, where Satoshi went to the Gym to challenge Misty. However, since Satoshi and his Pikachu had trouble swimming in the Gym's pool, they had to practice for a while in order to learn how to swim. Soon after, the Gym was attacked by a Team Rocket Grunt using a Gyarados, but Satoshi defeated the Grunt, driving him away. As a reward for saving the Gym, Misty gave Satoshi a Cascade Badge. She also gave Satoshi her Seel before the young Trainer left.

In the TCG

The Cerulean Gym was featured in the TCG as both a Japan exclusive Theme Deck and as a card. The following is a list of cards named Cerulean City Gym.

Related cardsCards listed with a blue background are only legal to use in the current Expanded format.Cards listed with a silver background are legal to use in both the current Standard and Expanded formats.

Trivia

In the English Generation I games, the Gym guide here refers to Pokémon of the Grass type as "plant Pokémon". In the English versions of Pokémon FireRed and LeafGreen, he instead mentions "Grass-type Pokémon". In the Japanese versions of the Generation I games and FireRed and LeafGreen, he mentions the Grass type itself, calling it the "Plant type" (Japanese: しょくぶつタイプ).

In Generation II, it is possible for the player to pick up the Machine Part from the Gym before learning of its location from the Team Rocket Grunt on Route 24. This is no longer the case in Generation IV, where the player must defeat the Grunt in a battle in order to make the Machine Part obtainable.